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Author Topic: HAM Musings  (Read 1373 times)

Offline Josh

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HAM Musings
« on: June 12, 2019, 2033 UTC »
The following was my response to a query on various HAM techniques and thought it grandiose and/or pompous enough to deserve a wider audience;





On antennas,
In my experience, verticals open and close a band due the low angle of radiation/reception, however sometimes horizontal polarisation gets stronger signals out of a given sig, usually some time between fadein and fadeout. Verticals are grand! It would be interesting to see if adding more radials helps any to the average HAM hf vertical, sometimes they do, sometimes they don't. I have a metal roofed garage that would be a good test bed for a vertical. Keep in mind that when you hear "120 radials is the best", that figure is quoted by people who have no idea where it came from. It came from some guys trying to get the most out of an ambc antenna they were building back in the 1920s, and they ran out of wire after 120 radials, so they decried 120 as optimal.

As to beams, they're the closest thing to cheating in HAM radio. :D

As to wrapping toroids, I prefer solid wire with a thick varnish coating.
They keep in place easier when winding, however offer more resistance to winding itself due the fact they're stiffer than stranded. Surplus Sales of Nebraska as well as other vendors carries triple coated wire for this, I suppose one will use whatever they have. I hope you watched the vid link* I sent you regarding how wire types can effect efficiency. For high power use, winding the toroid with fiberglass cloth will help add insulation between the turns and the toroid as well as keep the wire from chaffing on the sometimes less than smooth toroid - there's often a ridge where the parting lines of the toroid mold met. Using dual cores should help with the losses that show up as heat in the core, less core for the same input power means more heat due to losses, once a certain heat level is reached (normally not something one faces often) the core is permanently altered in the magnetic domain, lightning strikes will do much the same if not worse. 

RG8X is better than RG58, but not better than RG8, RG213, and other better grades. I prefer RG8X for mobile hf use, as in a vehicle. LMR types are getting cheaper and should be used unless one wants portability as a factor in coax selection, anything with a solid shield will not like to be flexed a lot before the shield tears. The higher the freq the better the coax should be, even 20m deserves 9913 or LMR400 type coax, especially when dealing with weak signals. I've been considering the cable tv coax types to use at hf for some time now, especially the orange stuff that can be directly buried.

I read a study done by USCG on their antenna sites and they found interaction between pretty much any coax running near other coax - a lot of coax they used was bundled together in places for sake of whatever reason, often in the air for long stretches, and this was on rx, they didn't bother with looking at it from the tx standpoint. They had been using stranded shield coax with multiple shields for a large number of rx arrays, but found leakage to be present in most if not all lines so they went with a solid shielding and buried and/or separated more of the lines as they could to reduce crosstalk - but solid shield was the key factor. After reading this, I got the idea 9913 or LMR400 is the way to go for the HAM. even on hf.

On how many turns of wire on a toroid, some say fill it as much as possible as the more turns you get means more flux/reluctance/permeability, others say you have to leave a gap of about 1/5 total winding covered but that may be for a different design outcome, can't remember. If you have the means to test, and it might not take much for testing at hf, try it and see how well it works. Check the in and out power levels as well as core heating, and of course swr and return loss. For those tests all you'd need to do ad hoc testing is a swr/power meter or two, dummy load or antenna, and a ir thermometer.

On bands above 20m.
I love 15m and 10m! 15 is open more often than 10 even when 10 is rolling, and you will find about as many if not more HAMs on 15 than 10. I think you will find more dx, and more fine business operating on 15 than on the other bands above 20m. A vertical or beam is best here, but a wire high up can work too if the ionsophere is forgiving as it determines the angle of radiation in the ionosphere in all cases - the antenna determines the initial angle of radiation - the lower the better for dx. On the lower freqs like 40 and 80 it becomes very hard to beat a full size dipole or sloper/inverted V. On the higher bands, when they seem closed, send a cq and see if some other geek is listening!

Keep in mind dx is there typically an hour before and an hour after local sunrise and sunset, as well as at the target location. Also, pretty much any station in darkness can hear any other station in darkness, propagation notwithstanding.

73!










*
https://www.youtube.com/watch?v=kMlKfHHR8FY
« Last Edit: June 12, 2019, 2039 UTC by Josh »
Conveniently located near Vincennes Indiana.

Offline IZS4

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Re: HAM Musings
« Reply #1 on: June 12, 2019, 2323 UTC »
I concur with this.

Offline Josh

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Re: HAM Musings
« Reply #2 on: June 17, 2019, 1821 UTC »
On baluns;

Balun winding
On the cancellation issue, you have to keep sense correct as you wind them or it can change the resultant z for better or worse, this is why one should test their design and construction, or at least follow tested designs to the letter. Also, some builders take their pairs of wire and give them a few twists per inch, I can't remember why they did this, probably to reduce or equalise distributed capacitance and perhaps to add some inductance.

While I'm enthusiastic about a dc ground antenna as provided by many balun designs, I prefer the simplicity of no balun other than a current choke to keep rf off the shield. With baluns you may run into issues where the swr isn't low, the balun can see voltages it can't support as insulation breaks down; I have this issue with my 1:1 dc grounded baluns, they can only handle low swr and the core may heat and shatter if you force operation on bands with high swr such as via a tuner.

Balun enclosures
I'd not want ferrite exposed to the environment for a few reasons, one is heating can be massive in sunlight and in theory a core could become hot enough in direct sunlight to permanently change its properties. Another is they're mostly iron and will rust if the core's not completely covered in epoxy or some other material, but you could ensure this easily enough. I suppose sufficient ice formation in or around the core could break them, they're very brittle.
Electrical boxes found at lowes and so on are commonly used to protect home made baluns. This is one reason I prefer commercial baluns and dipole center supports as most of them have enclosures I could never reproduce at home.

Uv would probably effect the insulating material of the wires eventually, I presume most insulated wire isn't intended to be exposed.
Conveniently located near Vincennes Indiana.